1. Field of the Invention
The present invention relates to a magnetoresistance effect element for reading the intensity of a magnetic field as a signal generated by a magnetic recording medium and the like.
2. Description of the Related Art
Currently, the a sensitivity of a magnetic sensor and the density of magnetic recording are increasing. With such increase, magnetoresistance effect magnetic sensors (hereinafter referred to as "MR" sensor) and magnetoresistance effect magnetic heads (hereinafter referred to as "MR" head) have been vigorously developed. The MR sensor and head read an external magnetic signal through the resistance change in a reading sensor comprising a magnetic material. Since the relative speed of the MR sensor or head to the magnetic recording medium does not depend on the reproducing output, a high sensitivity is achieved by the MR sensor and a high output is obtained by the MR head even in case of a high density magnetic recording.
However, with a MR sensor which comprises a conventional magnetic substance utilizing anisotropic magnetoresistance effect such as Ni.sub.0.8 Fe.sub.0.2, The magnetoresistance ratio .DELTA.R/R (which will be defined below) is only about 2 to 5%. Thus, a MR element having a larger magnetoresistance ratio is desired.
Recently, it was found that an artificial superlattice layer in which magnetic layers and nonmagnetic layers are alternately laminated such as a Fe/Cr system, induces a large magnetoresistance effect (cf. Phys. Rev. Lett., 61, 2472 (1988)). However, with this artificial superlattice layer, the external magnetic field at which the maximum resistance change is achieved is very large, namely ten or more KOe. Therefore, this artificial superlattice layer as such cannot be practically used.
Following the above artificial superlattice layer, a large magnetoresistance effect has also been found in various other systems. Among them, a Co/Cu artificial superlattice layer induces the magnetoresistance change, namely .DELTA.R/R of 60% or larger even in a small magnetic field change of about 10 KOe at room temperature (cf. Appl. Phys. Lett., 58, 2712 (1991)).
However, with the Co/Cu artificial superlattice layer, the intensity of the external magnetic field at which the resistance change occurs is too large, and it is difficult to practically use the artificial superlattice as the MR sensor or head.